Status Code 31
HIGH-HEAT PRESSURE SWITCH OR RELAY DID NOT CLOSE OR REOPENED - This status code can occur under the scenarios shown
below. Keep in mind that whenever the variable speed furnace control shuts unit down, gas remains off or shuts off immediately, inducer
continues running for 15 seconds, and if the blower is running, it remains running at low heat airflow or reduces to low heat airflow for the
selected off-delay. A miswired gas valve can cause this problem so make sure the BLUE wire goes to the gas valve M terminal and the
GREEN/YELLOW wire goes to the gas valve C terminal.
•
LOW HEAT PREPURGE OR STEADY-STATE - If the high heat pressure switch input turns ON the variable speed begins flashing status
code 31 and transitions to high heat. After the call for heat is satisfied and the blower off-delay is completed the control will stop displaying
status code 31.
•
HIGH HEAT
1. PREPURGE - If the high heat pressure switch HPS does not make within 45 seconds after the low-heat pressure switch LPS made the
variable speed begins flashing status code 31, shuts unit down, waits 2 minutes, stops flashing status code 31, and restarts heating cycle.
If high heat pressure switch HPS opens before ignition, the variable speed starts flashing status code 31 and ramps inducer RPM up until
the high heat pressure switch HPS remakes. When the high heat pressure switch HPS remakes the variable speed stops flashing status code
31 and continues heating cycle. If high heat pressure switch HPS does not remake within 45 sec after opening, the variable speed continues
flashing status code 31, shuts unit down, waits 2 minutes, stops flashing status code 31, and restarts heating cycle.
2. LOW HEAT TO HIGH HEAT TRANSITION - If the high heat pressure switch HPS fails to make within 45 seconds after high heat was
requested the variable speed furnace control shuts unit down and begins flashing status code 31. After the blower off-delay is completed
the variable speed will stop displaying status code 31 and if there is a call for heat, begin a new heating cycle. This new heating cycle will
be restricted to high heat.
3. STEADY-STATE - If the high heat pressure switch HPS opens the variable speed starts flashing status code 31 and ramps inducer RPM
up until the high heat pressure switch HPS remakes. When the high heat pressure switch HPS remakes the variable speed stops flashing
status code 31 and continues heating cycle. If high heat pressure switch HPS does not remake within 45 sec after opening, the variable speed
shuts the unit down and continues flashing status code 31. After the blower off-delay is completed the variable speed will stop displaying
status code 31 and if there is a call for heat, begin a new heating cycle. This new heating cycle will be restricted to high heat.
4. HIGH HEAT TO LOW HEAT TRANSITION - When using a 2-stage thermostat and W2 is de-energized, the high heat pressure switch
HPS must open within 5 seconds. If the high heat pressure switch HPS does not open within 5 seconds after W2 is de-energized, the
variable speed switches back to high heat and starts flashing status code 31. After the call for heat is satisfied and the blower off-delay
is completed the variable speed will stop displaying status code 31.
STEP
ACTION
YES
NO
GO TO
1
Turn power off, remove blower access panel, and discon-
nect R thermostat lead.
2
2
Turn power on and depress door switch. Use a piece of
tape to hold switch closed.
3
3
Jumper R, W/W1, and W2 thermostat terminals.
4
4
Wait 90 seconds before proceeding to the next step.
5
5
Does status code 31 flash?
9
6
6
Does a different status code flash?
7
34
7
Go to page number indicated in the Index for the section
covering the status code.
INDEX
8
Go to page number indicated in Index for CLEANUP AND
START-UP INSTRUCTIONS.
INDEX
9
Is 24-vac across GRAY wire on the high heat pressure
switch HPS and COM-24V on variable speed furnace con-
trol?
15
10
10
Is 24-vac across connector terminal PL1-12 and C
OM
-24V
on variable speed furnace control?
11
13
11
You have an open wire or bad terminal on the GRAY wire
from the variable speed furnace control to the high heat
pressure switch HPS.
12
12
Repair or replace the main wire harness.
8
13
Replace the variable speed furnace control.
8
14
The problem is caused by reversed vent and combustion-air
pipes or some other moist air entering combustion-air pipe.
32
15
Does the high heat pressure switch HPS make, then break
several times at start of cycle before faulting out?
16
17
16
The problem is either a sag in vent pipe or a clogged drain
trap or line. Also check for improperly plumbed drainage
tubing within furnace.
32
17
Is 24-vac across BROWN wire on the high heat pressure
switch HPS and COM-24V on variable speed furnace con-
trol?
18
20
18
Is 24-vac across connector terminal PL1-3 and C
OM
-24V on
variable speed furnace control?
13
19
21
